Abstract: Recycling of spent lithium iron phosphate (LiFePO₄, LFP) cathode materials is an encouraging way of resource reuse to alleviate environmental issues. Nevertheless, traditional regeneration techniques are usually too complicated and difficult to industrialize, especially no longer applicable to severely degraded LFP cathodes. Herein, we report a novel physically confined-domain pressure sintering method for large-scale direct regeneration of severely degraded spent LFP cathodes (<20 % residual capacity). By constructing physically confined domains, the interface interaction between lithium ions (Li⁺) and the cathode is enhanced and the potential barrier during relithiation is thus decreased, facilitating the insertion of Li⁺ into vacancies. The internal residual conductive carbon builds a reduced circumstance to promote the conversion of the Fe (III) to Fe (II) phase and reduce the Li-Fe anti-site (Fe_Li) defects. The broken small particles (heterogeneous phase) are in-situ re-synthesized into complete olivine structures driven by external pressures. The capacity retention of the regenerated LFP cathodes was 88.8 % after 1500 cycles at 5 C. This work provides one-step, highly efficient, and scalable technology for direct regeneration of severely degraded LFP into high-performance cathode materials.

Key words: LiFePO₄, Physically confined-domain, Direct regeneration, Severely degraded LFP cathodes